diff --git a/roles/dev_env/molecule/default/converge.yml b/roles/dev_env/molecule/default/converge.yml
index cf2227a..6539769 100644
--- a/roles/dev_env/molecule/default/converge.yml
+++ b/roles/dev_env/molecule/default/converge.yml
@@ -7,9 +7,38 @@
     dev_env__users:
       - tester
   pre_tasks:
+    # `always` so the test user exists even under a partial `--tags` converge.
     - name: Create a test user to receive the environment
       ansible.builtin.user:
         name: tester
         create_home: true
+      tags: [always]
   roles:
     - role: dev_env
+
+# Partial-tags regression guard (O8): apply only the `config` concern to a fresh user.
+# The dev_env__home preflight is tagged `always`, so a config-only run must still resolve
+# the home dir and stow the dotfiles. Run the true partial path with:
+#   molecule converge -- --tags config
+# (a full `molecule test` runs every tag, which still exercises this play idempotently).
+- name: Converge — config concern only, fresh user
+  hosts: all
+  become: true
+  gather_facts: true
+  vars:
+    dev_env__users:
+      - tagtester
+  pre_tasks:
+    # `always` so the test user exists even under a partial `--tags config` converge.
+    - name: Create a second test user for the config-only path
+      ansible.builtin.user:
+        name: tagtester
+        create_home: true
+      tags: [always]
+  tasks:
+    - name: Apply dev_env restricted to the config concern
+      ansible.builtin.include_role:
+        name: dev_env
+        apply:
+          tags: [config]
+      tags: [config]
diff --git a/roles/dev_env/molecule/default/verify.yml b/roles/dev_env/molecule/default/verify.yml
index 04ac53a..7ebd832 100644
--- a/roles/dev_env/molecule/default/verify.yml
+++ b/roles/dev_env/molecule/default/verify.yml
@@ -71,3 +71,18 @@
           - dev_env__dots.results[3].stat.exists
           - dev_env__dots.results[4].stat.exists
         fail_msg: dotfiles not stowed or omz/tpm not cloned
+
+    # Partial-tags regression guard (O8): the config-only converge play provisioned
+    # `tagtester`. Its stowed .zshrc proves dev_env__home resolved (the `always` preflight)
+    # and stow (a `config` task) ran without the `users`/`packages` concerns.
+    - name: Stat the config-only user's stowed .zshrc
+      ansible.builtin.stat:
+        path: /home/tagtester/.zshrc
+      register: dev_env__tagtester_zshrc
+
+    - name: Assert the config concern alone resolved home and stowed dotfiles
+      ansible.builtin.assert:
+        that:
+          - dev_env__tagtester_zshrc.stat.exists
+          - dev_env__tagtester_zshrc.stat.islnk
+        fail_msg: config-only run did not resolve dev_env__home / stow dotfiles for tagtester
diff --git a/roles/dev_env/tasks/main.yml b/roles/dev_env/tasks/main.yml
index 6e15ee6..ce9b6eb 100644
--- a/roles/dev_env/tasks/main.yml
+++ b/roles/dev_env/tasks/main.yml
@@ -7,21 +7,40 @@
     cache_valid_time: 3600
   tags: [packages]
 
+# `apply: tags:` propagates the concern tag onto the INCLUDED tasks — without it a tag on
+# a dynamic include_tasks only selects the include itself, not its (untagged) contents, so
+# `--tags <concern>` would run nothing (Ansible gotcha; mirrors roles/base/tasks/main.yml).
 - name: Install Neovim (pinned release)
-  ansible.builtin.include_tasks: neovim.yml
+  ansible.builtin.include_tasks:
+    file: neovim.yml
+    apply:
+      tags: [packages]
   tags: [packages]
 
 - name: Install oh-my-posh prompt (pinned release)
-  ansible.builtin.include_tasks: oh_my_posh.yml
+  ansible.builtin.include_tasks:
+    file: oh_my_posh.yml
+    apply:
+      tags: [packages]
   tags: [packages]
 
 - name: Install Node.js (pinned release)
-  ansible.builtin.include_tasks: nodejs.yml
+  ansible.builtin.include_tasks:
+    file: nodejs.yml
+    apply:
+      tags: [packages]
   tags: [packages]
 
+# per_user.yml resolves dev_env__home (tagged `always`, below) then runs both the `users`
+# (login shell) and `config` (dotfiles/stow) concerns; tag + apply both so either
+# `--tags users` or `--tags config` reaches in and the home-dir preflight always runs.
 - name: Configure each developer user
-  ansible.builtin.include_tasks: per_user.yml
+  ansible.builtin.include_tasks:
+    file: per_user.yml
+    apply:
+      tags: [users, config]
   loop: "{{ dev_env__users }}"
   loop_control:
     loop_var: dev_env__user
     label: "{{ dev_env__user }}"
+  tags: [users, config]
diff --git a/roles/dev_env/tasks/per_user.yml b/roles/dev_env/tasks/per_user.yml
index 6a69705..e0b854c 100644
--- a/roles/dev_env/tasks/per_user.yml
+++ b/roles/dev_env/tasks/per_user.yml
@@ -1,12 +1,17 @@
 ---
+# `always`: dev_env__home must resolve on every entry into per_user.yml, including a
+# partial `--tags users` or `--tags config` run — the dotfile/stow (config) and login-shell
+# (users) tasks below all depend on it, so it must never be filtered out (ADR-019).
 - name: Look up account for {{ dev_env__user }}
   ansible.builtin.getent:
     database: passwd
     key: "{{ dev_env__user }}"
+  tags: [always]
 
 - name: Resolve home directory for {{ dev_env__user }}
   ansible.builtin.set_fact:
     dev_env__home: "{{ getent_passwd[dev_env__user][4] }}"
+  tags: [always]
 
 - name: Set login shell to zsh for {{ dev_env__user }}
   ansible.builtin.user: